packages: Add the channel .go files to the search path.

Until now %LOAD-COMPILED-PATH would wrongfully contain:

  CHANNEL/share/guile/site/X.Y

for each channel, thereby ignoring all the .go files of channels.  This
fixes it so that %LOAD-COMPILED-PATH instead contains:

  CHANNEL/lib/guile/X.Y/site-ccache

* guix/describe.scm (current-channel-entries): New procedure.
(package-path-entries): Change to return the %LOAD-COMPILED-PATH entries
as a second value.
* gnu/packages.scm (%package-module-path): Expect two values from
'package-path-entries' and augment %LOAD-COMPILED-PATH accordingly.

gnu/packages.scm

@@ -155,23 +155,26 @@ flags."
   ;; Search path for package modules.  Each item must be either a directory
   ;; name or a pair whose car is a directory and whose cdr is a sub-directory
   ;; to narrow the search.
-  (let* ((not-colon   (char-set-complement (char-set #\:)))
-         (environment (string-tokenize (or (getenv "GUIX_PACKAGE_PATH") "")
+  (let*-values (((not-colon)
+                 (char-set-complement (char-set #\:)))
+                ((environment)
+                 (string-tokenize (or (getenv "GUIX_PACKAGE_PATH") "")
                                   not-colon))
-         (channels    (package-path-entries)))
+                ((channels-scm channels-go)
+                 (package-path-entries)))
     ;; Automatically add channels and items from $GUIX_PACKAGE_PATH to Guile's
     ;; search path.  For historical reasons, $GUIX_PACKAGE_PATH goes to the
     ;; front; channels go to the back so that they don't override Guix' own
     ;; modules.
     (set! %load-path
-      (append environment %load-path channels))
+      (append environment %load-path channels-scm))
     (set! %load-compiled-path
-      (append environment %load-compiled-path channels))
+      (append environment %load-compiled-path channels-go))
 
     (make-parameter
      (append environment
              %default-package-module-path
-             channels))))
+             channels-scm))))
 
 (define %patch-path
   ;; Define it after '%package-module-path' so that '%load-path' contains user

guix/describe.scm

@@ -65,18 +65,27 @@ lives in, or #f if this is not applicable."
        (let ((manifest (profile-manifest profile)))
          (manifest-entries manifest))))))
 
-(define package-path-entries
+(define current-channel-entries
   (mlambda ()
-    "Return a list of package path entries to be added to the package search
-path.  These entries are taken from the 'guix pull' profile the calling
-process lives in, when applicable."
+    "Return manifest entries corresponding to extra channels--i.e., not the
+'guix' channel."
+    (remove (lambda (entry)
+              (string=? (manifest-entry-name entry) "guix"))
+            (current-profile-entries))))
+
+(define (package-path-entries)
+  "Return two values: the list of package path entries to be added to the
+package search path, and the list to be added to %LOAD-COMPILED-PATH.  These
+entries are taken from the 'guix pull' profile the calling process lives in,
+when applicable."
   ;; Filter out Guix itself.
-    (filter-map (lambda (entry)
-                  (and (not (string=? (manifest-entry-name entry)
-                                      "guix"))
-                       (string-append (manifest-entry-item entry)
+  (unzip2 (map (lambda (entry)
+                 (list (string-append (manifest-entry-item entry)
                                       "/share/guile/site/"
-                                      (effective-version))))
+                                      (effective-version))
+                       (string-append (manifest-entry-item entry)
+                                      "/lib/guile/" (effective-version)
+                                      "/site-ccache")))
                (current-profile-entries))))
 
 (define (package-provenance package)